Scroll machines are becoming more and more popular for use as compressors in both refrigeration as well as air conditioning and heat pump applications due primarily to their capability for extremely efficient operation. Generally, these machines incorporate a pair of intermeshed spiral wraps, one of which is caused to orbit relative to the other so as to define one or more moving chambers which progressively decrease in size as they travel from an outer suction port toward a center discharge port. An electric motor is provided which operates to drive the orbiting scroll member via a suitable drive shaft.
Because scroll compressors depend upon a seal created between opposed flank surfaces of the wraps to define successive chambers for compression, suction and discharge valves are generally not required. However, when such compressors are shut down, either intentionally as a result of the demand being satisfied, or unintentionally as a result of power interruption, there is a strong tendency for the pressurized chambers and/or backflow of compressed gas from the discharge chamber to effect a reverse orbital movement of the orbiting scroll member and its associated drive shaft. This reverse movement often generates objectionable noise or rumble and can possibly damage the compressor.
A primary object of the present invention resides in the provision of a very simple and unique unloader wedge cam which can be easily assembled into a conventional gas compressor of the scroll type without significant modification of the overall compressor design, and which functions at compressor shut-down to unload the orbiting scroll so that the discharge gas pressure can balance with the suction gas pressure. The present invention allows discharge gas pressure to drive the compressor in the reverse direction while the wedge cam separates the spiral wraps of the orbiting and non-orbiting scroll members thus eliminating the normal shut-down noise associated with the reverse rotation.
A further object of the present invention concerns the provision of an unloader wedge cam which can accommodate without damage extended powered reversal of the compressor, which can occur when a miswired three-phase motor is the power source.
The primary embodiment of the present invention achieves the desired results utilizing a very simple device which is rotationally driven by the compressor running gear and which under the proper conditions wedges between a fixed wall of the bearing housing and the hub of the orbiting scroll to physically prevent the flank surface of the spiral wraps from contacting during reverse rotation. The device is a wedge cam which is journaled on the upper end of the crankshaft.
These and other features of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings.